NEDD8 Deamidation Inhibits Cullin RING Ligase Dynamics.

Cullin-RING ligases (CRLs) are essential for ubiquitination pathways that regulate key cellular functions. These enzymes are activated by NEDD8 conjugation, which induces conformational shifts in the Cullin C-terminal domain (CTD). Prior research has shown that NEDD8 binding promotes an open CTD structure, allowing interaction with RING E3 ligases. However, the role of non-covalent interactions in stabilizing this active conformation remains unclear. Enteric bacterial toxins like Cycle inhibitory factor (Cif) are known to inactivate CRLs by deamidating NEDD8 at glutamine 40. This gap motivated the current investigation into how deamidation affects NEDD8 structure and CRL dynamics. No prior work had resolved the molecular consequences of this modification on NEDD8/WHB interactions. The uncertainty around the mechanism of Cif-induced CRL inhibition drove the need for structural and dynamic studies.

The study aimed to determine whether non-covalent interactions between NEDD8 and the Cullin CTD are sufficient to stabilize the active conformation of CRLs. Researchers also sought to clarify how glutamine deamidation by Cif disrupts this process. By combining molecular dynamics simulations with NMR spectroscopy, the team investigated the structural and dynamic effects of NEDD8 deamidation. The specific problem addressed was the lack of clarity on whether non-covalent interactions alone could maintain the open CTD conformation. The motivation for this work stemmed from the known role of Cif in modulating host cell signaling through CRL inhibition. Understanding the molecular consequences of deamidation could provide insights into bacterial pathogenesis and ubiquitin signaling. The study focused on the WHB subdomain of the CTD and its interactions with NEDD8.

The researchers used atomistic molecular dynamics (MD) simulations to model the conformational dynamics of the Cullin C-terminal domain (CTD) in the presence and absence of NEDD8. They also employed NMR spectroscopy to validate structural changes in deamidated NEDD8. The simulations tracked interactions between NEDD8 and the 4HB/αβ subdomains of the CTD. The team analyzed how these interactions influence the stability of the open conformation. They compared wild-type NEDD8 with the deamidated variant at glutamine 40. The simulations provided insights into the role of non-covalent interactions in CRL activation. The NMR data confirmed the formation of a new salt bridge in deamidated NEDD8. The combination of computational and experimental approaches allowed for a detailed analysis of the structural and dynamic effects of deamidation.

The simulations revealed that NEDD8 forms non-covalent interactions with the 4HB/αβ subdomains of the Cullin CTD, promoting an open conformation. These interactions were found to be sufficient to stabilize the active state of the CTD. The study showed that deamidation at glutamine 40 in NEDD8 disrupts these interactions. The deamidated NEDD8 formed a new intramolecular salt bridge, which destabilized the NEDD8/WHB complex. This structural change reduced the stability of the open CTD conformation. NMR spectroscopy confirmed the presence of the salt bridge in deamidated NEDD8. The results suggest that deamidation inhibits CRL activity by weakening the NEDD8/WHB interaction. The findings indicate that non-covalent interactions play a key role in maintaining the active conformation of CRLs.

The authors concluded that non-covalent interactions between NEDD8 and the Cullin CTD are sufficient to stabilize the open conformation of CRLs. Deamidation at glutamine 40 in NEDD8 disrupts these interactions by forming a new intramolecular salt bridge. This structural change destabilizes the NEDD8/WHB complex, leading to reduced CRL activity. The findings suggest that Cif-induced deamidation inhibits CRL function by altering the conformational dynamics of the CTD. The study highlights the importance of non-covalent interactions in maintaining the active state of CRLs. The results provide a molecular mechanism for how bacterial toxins modulate host cell signaling. The authors propose that the salt bridge formation in deamidated NEDD8 is a key factor in CRL inactivation. These conclusions are based on the combined use of MD simulations and NMR spectroscopy.